Electronic controller for automatic leveling system

ABSTRACT

In preferred form, an electronic control for an electrically operated automatic vehicle leveling system which includes a relay coil and a solenoid operated valve coil that are both connected to one terminal of a three terminal solid-state switching device in the form of a pair of transistors in a Darlington configuration. The base emitter junction of the Darlington pair is connected to a RC timing circuit through a low cost switching transistor. An undamped height sensor switch connects the charging circuit to the positive terminal of a vehicle battery and the switching transistor closes to charge a capacitor of the RC circuit from a negative reference voltage to a positive turn on voltage at the base of the Darlington pair. Following a predetermined time delay the Darlington pair is turned on to complete an energization circuit for one or the other of the coils. If the undamped switch opens before the end of a time delay cycle, the positive side of the capacitor is recharged to the battery voltage through a reset circuit to prevent normal road movements from affecting the operation of the circuit.

United States Patent [72] Inventor James 0. Elliott Xenia, Ohio [21]Appl. No. 19,307 [22] Filed Mar. 13, 1970 [45] Patented Nov. 30, 1971[73] Assignee General Motors Corporation I Detroit, Mich.

a [54] ELECTRONIC CONTROLLER FOR AUTOMATIC LEVELING SYSTEM 4 Claims, 4Drawing Figs. [52] US. Cl 317/141 S, 317/1485 R [51] Int. Cl ..l-l0lh47/32, HO 1 h 47/18 [50] Field ofSearch 317/141 S, g 142, 148.5 [56]References Cited UNITED STATES PATENTS 2,867,754 1/1959 OBleness 317/141S 3,334,243 8/1967 Cooper Primary Examiner-L. T. Hix Attorneys-W. S.Pettigrew and .I. C. Evans ABSTRACT: In preferred form, an electroniccontrol for an electrically operated automatic vehicle leveling systemwhich includes a relay coil and a solenoid operated valve coil that areboth connected to one terminal of a three terminal solid-state switchingdevice in the form of a pair of transistors in a Darlingtonconfiguration. The base emitter junction of the Darlington pair isconnected to a RC timing circuit through a low cost switchingtransistor. An undamped height sensor switch connects the chargingcircuit to the positive terminal of a vehicle battery and the switchingtransistor closes to charge a capacitor of the RC circuit from anegative reference voltage to a positive turn on voltage at the base ofthe Darlington pair. Following a predetermined time delay the Darlingtonpair is turned on to complete an energization circuit for one or theother of the coils. 1f the undamped switch opens before the end of atime delay cycle, the positive side of the capacitor is recharged to thebattery voltage through a reset circuit to prevent normal road movementsfrom affecting the operation of the circuit.

PATENTEUuuv 3019?: 3, 624.456 SHEET 1 OF 2 INVIEN'IOR.

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ATTORNEY ELECTRONIC CONTROLLER FOR AUTOMATIC LEVELING SYSTEM Thisinvention relates to electronic controllers and more particularly toelectronic timers having means for selectively energizing a plurality ofseparate loads following a predetermined time delay.

Automatic electrically operated vehicle-lcveling systems include anelectric motor driven compressor which either pumps up or exhausts fluidfrom a pair of auxiliary load sup porting fluid springs connectedbetween the sprung and unsprung mass of a vehicle to maintain apredetermined height relationship therebetween when the primarysuspension springs are either shortened or lengthened because of thechange of the vehicle load.

In certain ones of these automatic leveling systems there are twoseparate electrically energizable components, for example, a relayoperated motor control switch that connects the compressor drive motorto a power source during, for example, an exhaust phase of operation andan electrically energizable coil for a solenoid valve that will connecta pressure source to the fluid springs during a pump up phase ofoperation.

In some automatic leveling systems the components are connected to thepower source through a mechanically damped height sensor switch that isonly responsive to a sustained change in the height relationship betweenthe sprung chassis of the vehicle and an unsprung portion thereof suchas the axle housing of the rear suspension assembly of the vehicle.

Such damped mechanical valves require connection of separate linkagebetween an operating arm of the valve and an adjacent portion of thesprung and unsprung mass. Such arrangements are comparatively costly.

Other vehicle leveling systems include an undamped electrical heightsensor switch that may require a like linkage. Such arrangements areless costly, however, they respond to normal road movements to operatethe system through exhaust and pump up phases when vehicle heightcorrection is not required. I

Accordingly, an object of the present invention is to provide animproved all-electric controller for an automatic vehicleleveling systemwherein a low-cost undamped double-pole, double-throw switch is used tosense the height relationship between the sprung and unsprung masses ofthe vehicle and where a timing circuit and three-terminal solid-stateswitching device are included in circuit with the undamped switch andthe control components of the leveling system to prevent operationthereof in response to normal road movements.

Still another object of the present invention is to provide a motorcontrol circuit having a relay-operated switch with a coil electricallyconnected to a three terminal switching device which has a timingcircuit electrically connected to a power source and operative toproduce a predetennined time delay before operation of the motor controlrelay coil and wherein the timing circuit includes a switchingtransistor which is closed by a signal to initiate the time delay andwhich is opened for resetting the timing circuit anytime that the signalthereto is interrupted.

Still another object of the present invention is to provide a low costsolid state timer including a static amplifier having its base emitterjunction connected to a timing circuit including a capacitor having itsnegative side connected to the base and its positive side connectedthrough a low-impedance path to a power source and wherein a highimpedance in the timing circuit provides a predetermined long-durationdelay for charging the negative side of said capacitor to a fullpositive charge when a current path is completed through the timingcircuit; and wherein when the timing circuit is disconnected the lowimpedance path to the positive side of the capacitor will react thecapacitor to a full charge on the opposite side thereof at a time ratiocorresponding to that of the impedance in the timing circuit and theimpedance in the low-impedance connection to the positive side of thecapacitor.

Still another object of the present invention is to provide anarrangement as set forth in the immediately preceding object wherein thetiming circuit includes a capacitor having its negative sideelectrically connected to the control terminal of the static amplifierand the positive side thereof electrically connected to a ground pointthrough a low-cost NPN-transistor and wherein the circuit includes animpedance path to the base of the NPN-transistor for turning it on eachtime a height sensor switch connects an electrical component to thepower source to initiate a delay period which prevents energization ofthe electrical components of a leveling system by normal road movementsof the vehicle.

Still another object of the present invention is to provide an improvedelectronic switching device and timer for selectively operating aplurality of separate loads including a power static amplifier; aresistance capacitor circuit electrically connected to the controlterminal of said amplifier and to a switching transistor for reset; acircuit energized when the power supplies are connected to a powersource for turning on the transistor to start charging of the capacitor;said amplifier having its cathode anode terminals electrically connectedto each of the energizable components for completing a current paththrough the component that is connected to the power supply followingthe delay period; a pair of diodes each connected between the electricalcomponent that is energized and the charging circuit for the capacitorare operative to prevent cross current flow to the other of theelectrical components when deenergized; and means for resetting thecharging circuit when the switching transistor is off including arelatively low impedance path from a power source to the positive sideof the capacitor of the charging circuit to produce a reset time that issubstantially less than the time delay period of the circuit.

These and other objects are attained in one working embodiment of theinvention in a system that includes two spaced apart auxiliary loadsupporting combination shock absorber and air spring units each havingtheir top and bottom mounts adapted to be connected respectively betweenthe lower frame of the vehicle body and the rear axle housing of therear suspension of the vehicle. The system includes a double pole,double throw switch that is strapped on one side of one of the units tosense the height relationship between the top of the shock absorber anda surrounding dust shield portion of the shock absorber which in turnrepresents the height relationship between the vehicle body and the axlehousing.

When the vehicle body is above a desired height relationship the switchis in a first position wherein an electric motor is energized to pumpdown both of the auxiliary load carrying air springs on the combinationunit and to increase the pressure within a storage tank. When thevehicle body is below the desired height relationship the switch ispositioned to energize a solenoid valve for connecting the pressurizedtank with the air spring means to increase the pressure level therein;to raise its load supporting capacity; to return the vehicle body to adesired height relationship with the axle housing.

The switch is an undamped mechanism that electrically connects first andsecond electrical components in the system to the positive terminal ofthe vehicle battery. An electronic control module receives a signal fromthe switch each time it connects one or the other of the components tothe battery to charge a timing circuit that delays energization of astatic amplifier that powers the electrical components in the system.

The time delay is selected to prevent operation of the electricalcomponents in response to ordinary vehicle road movements.

A switching transistor is turned on each time one of the components isinvention; to the power supply to complete the timing circuit. When theundampened switch on the air spring is turned ofi the switchingtransistor is turned off and the timing circuit is reset. Thus, only asustained load change that maintains the undamped height sensor switchcontinuously closed will cause the timing circuit to condition thestatic amplifier conductive thereby to energize one of the other of thecomponents to produce a change in the pressure level of the air springsfor leveling.

Further objects and advantages of the present invention will be apparentfrom the following description, reference being had to the accompanyingdrawings wherein a preferred embodiment of the present invention isclearly shown.

FIG. 1 is a diagrammatic view of a leveling system including the presentinvention;

FIG. 2 is an electric circuit diagram of a control system for regulatingthe electrical components of the system of FIG. 1;

FIG. 3 is a chart shown the charge rate of a capacitor in the presentinvention;

FIG. 4 is a chart showing reset and time delay features of the controlcircuit of the present invention.

Referring now to the drawings, in FIG. 1 a fully automatic electricclosed-loop vehicle-leveling system is illustrated. It includes a pairof combination shock absorber and air spring units 12, 14 each of whichincludes a top end mount assembly 16 and a bottom end mount assembly 18.The top end mount assembly 16 is adapted to be connected to the bottomframe of a vehicle body which represents a sprung mass. The bottom endmount 18 is adapted to be connected to a portion of the rear suspensionassembly, for example, the rear axle housing which represents anunsprung mass in the system.

Both of the units l2, 14 represent an auxiliary load supporting devicethat is associated with a primary load supporting spring (not shown)that maintains a predetermined curb height between the vehicle body andthe axle housing when the vehicle is unloaded.

In order to maintain this predetermined curb height or any otherpredetennined height relationship, the vehicle-leveling system 10 isoperated to vary the pressure in a variable volume pressurizable fluidchamber 20 of each unit 12, 14 fonned between a dust tube 22 closed atits upper end by a cap 24 and an outer shock absorber cylinder 26.

In the illustrated arrangement the shock absorber also includes a pistonrod 28 that moves exteriorly of cylinder 26.

The chamber 20 is closed by a flexible sleeve 30 that has one endthereof fastened to the open lower end of the dust tube 22 by a clampring 32 and the opposite end thereof secured to the outer periphery ofthe cylinder 26 by a like clamp ring (not shown).

The chamber 20 of the unit 14 has an inlet fitting 36 thereon and anoutlet fitting 38 that is joined by a crossover tube 40 to an inletfitting 42 to the chamber 20 of the unit 12. A common exhaust and supplyconduit 44 has one end thereof connected to the inlet fitting 36 and theopposite end thereof connected to a fitting 46 on a combination valveand fluid supply assembly 48.

1n the illustrated arrangement the assembly 48 includes a housing 50that is supported in an opening 52 of a pressurized storage tank 54. 1

An electric compressor drive motor 56 is supported within the tank 54.It drives an air compressor 58 having an inlet 60 and an outlet 62.

The outlet 62, more particularly, is in direct communication with theinterior of tank 54 and the inlet 60 is connected to one end of aspring-reinforced suction tube 64 that has the opposite end thereofconnected to a tube member 66 depending from the housing 50.

1n the illustrated arrangement the electrical drive motor 56 iscontrolled by a relay operated switch 68 that is supported on one sideof a circuit board 70 along with an electronic control module 72 to bedescribed.

The relay 68 constitutes a first electrically energizable component forcontrolling the operation of the leveling system 10.

Additionally, the system includes a solenoid operated valve 74 (see FIG.2) which communicates the interior of tank 54 with the conduit 44 when acoil 76 thereof is energized.

The coil 76 constitutes a second electrically energizable component forregulating the operation of the leveling system l0.

The system further indicates a height sensor switch 78 that is held onone side of the unit 14 by a strap 80 to position a contact carryingmovable arm 86 with respect to a first pair of motor contacts 88 and asecond pair of solenoid contacts 90 both of which are maintainednormally open and are bridged when the movable arm 86 is in engagementtherewith.

The height sensor switch 78 is a low cost non-damped unit that senseseach relative movement of the dust tube 22 with respect to the shockabsorber cylinder 26 which reflects normal road movements between thesprung and unsprung mass of the vehicle.

In accordance with certain principles of the present invention theelectronic control module 72 includes means for producing apredetermined time delay in the system to prevent operation of thesystem by normal road movements of the vehicle. Additionally, the module72 includes means that constitute a controller for the motor 56 toenergize it following periods when the vehicle is unloaded thereby tocause the auxiliary load supporting devices 12, 14 to be pumped down tolevel the vehicle.

A further feature is that the module 72 includes means for controllingthe electrical solenoid to be operative following a sustained additionof load to the vehicle to pump up or pressurize the auxiliary loadsupporting devices 12, 14 to correct for spring compression that wouldlocate the chassis of the vehicle below a predetermined heightrelationship with respect to an unsprung mass portion of the vehicle.When the solenoid operated valve 74 is energized it directs apredetermined amount of air from the interior of the pressurized tank 54into the variable volume pressurizable chambers 20 of the devices 12,14.

The module 72 is more particularly set forth in the control circuit ofFlG. 2 which is illustrated as including a DC battery 92, for example, a12 volt rated vehicle battery. Additionally, the circuit includes anignition switch 94 and the double-pole double-throw switch 90 operatedby the height sensor 78 on the side of the device 10.

The circuit includes a first power circuit for control of the motorincluding a conductor 96 connected to the positive terminal of thebattery 92 and a conductor 98 electrically connected to one terminal ofnormally open switch 88. The other terminal thereof is electricallyconnected by a conductor 99 to one side of a motor relay coil 100 thathas the opposite side thereof electrically connected by a conductor 102thence through a conductor 104 to the anode terminal of a solid-stateswitching device of a Darlington amplifier 106 that is maintainednormally off. When device 106 is electrically conductive the coilcircuit is completed through a conductor 108 to ground.

Additionally, the circuit includes a solenoid coil power circuit fromconductor 96 thence through a conductor 110 to the ignition switch 94thence through a conductor 112 to one terminal of second normally openswitch 90 that has the other terminal thereof connected by a conductor114 to one side of a solenoid valve coil 116 surrounding a valvearmature 118.

The opposite side of the coil 116 is connected by a conductor 120 to thepreviously described portion of the electrical circuit through the solidstate switching device 106 thence to ground.

The solid state switching device 106 is under the control of a timingcircuit that is electrically connected to both of the aforementionedpower circuits under the control of the height sensor 78.

The timing circuit more particularly includes, in the case of the motorpower circuit, a conductor 122 from conductor 99 which is connected to adiode 124 which in turn is electrically connected to a resistor 126thence to the negative terminal of a capacitor 128. Additionally, aconductor 130 electrically connects the base or control terminal of thesolid-state switching device 106 to the RC timing circuit represented bythe resistance 126 and the capacitor 128.

The RC circuit is completed from the positive terminal of the capacitor128 through a NPN test transistor 132 that has its emitter electricallyconnected by a conductor 134 to conductor 108 to ground.

In the case of the solenoid coil circuit the timing circuit isconstituted by a conductor 136 that is electrically connected to oneside of a diode 138 which has its opposite side electrically connectedby a crossover conductor 140 to the aforementioned RC timing circuitincluding the resistor 126, the capacitor 128 and the normally closedreset transistor 132.

Additionally, the control circuit includes a signal circuit to thetransistor 132 which is energized if either of the aforementioned motorpower or solenoid power circuits are completed by the height sensorswitch 78. More particularly, it includes a conductor 142 electricallyconnecting the crossover conductor 140 to one side of a resistor 144which has the opposite side thereof electrically connected by aconductor 146 to the base of the transistor 132. A resistor 148electrically connects the base-emitter junction of the transistor 132 tothe conductor 108 to groun In addition, the circuit includes a circuitfrom the positive terminal of the battery 92 to a conductor 150 which iselectrically connected by conductor 152 to one contact of a relayoperated motor control switch 68 which has the other contact thereofelectrically connected by a conductor 154 to one side of the electricdrive motor 56 which has the opposite side thereof electricallyconnected by conductor 156 to ground. A contact carrying armature 158 isoperated to close the relay contacts when the coil is energized tocomplete the motor circuit.

Additionally, the conductor 150 is electrically connected to one end ofa resistor 160 which in turn is electrically connected by conductor 162to define a low-impedance path to a junction between the positiveterminal of the capacitor 128 and the collector of the transistor 132.

Operation of the system produces a signal when the vehicle is ridingabove or below a predetermined normal riding level; the signal is fromthe positive terminal of the battery 92 through height sensor 78 thencethrough either the power circuit of the motor relay coil orthat of thesolenoid coil to the RC timing circuit defined by resistor 126,capacitor 128 and transistor 132. Furthermore, the circuit includesmeans to operate either the solenoid valve or the compressor in responseto a continued vehicle riding height signal representing a change inloading of the vehicle.

Under a no signal condition when the vehicle is level and the movablecontact of the sensor 78 is positioned in open relationship with respectto both the switch contacts 88 and the switch contacts 90, thetransistor 132 is turned off thereby acting as an open switch to ground.The capacitor 128 during this period is charged from battery 92,conductor 150, the resistance 160 to the positive terminal of thecapacitor. The level of charge on the positive terminal of the capacitor128 will equal that of the voltage of the battery 92 which can, in thecase of a standard l2 volt rated battery, vary in a range from ID tovolts depending upon the condition of the battery.

When either the switch 88 in the motor power circuit or the switch 90 inthe solenoid power circuit is closed, the transistor 132 is immediatelyturned on by current applied to its base from either of the powercircuits. This completes the abovedefined resistance capacitor chargingcircuit.

At this point in the system operation, the capacitor voltage at the baseof the Darlington pair-106 is now a negative voltage with reference toground an amount equal to the battery voltage.

Additionally, the capacitor 128 is connected to ground through thetransistor 132. As shown in FIG. 3, the capacitor charges in theopposite direction from this minus battery voltage to approximately 1volt positive. When a certain predetermined positive voltage is reached,there is a base current flow which turns on the Darlington pair 106. Itconducts from its anode to its cathode terminal and provides a currentpath to ground for either the relay coil 100 or solenoid coil 116. Thedelay time is measured from the time the signal turns on the resistor126. The large swing transistor 132 to the time that the Darlingtonamplifier 106 is conductive. The delay time due to negative voltagefiring spreads the total delay time without the need for an expensivehigh mfd. rated capacitor. I

The charging time of the capacitor 128 also is set by resistor 126 whichis large with respect to the other resistors in the network. When thesensor switch 78 has its switches 88, opened, the transistor 132immediately turns ofi". The resistor 160 is relatively small compared tothe resistor 126 and the capacitor 128 thereby is recharged to thenegative battery voltage in a very short length of time as compared tothe time period following closure of the contacts 88, 90 to reach theDarlington turn on voltage. This reset characteristic is set forth inthe graph of FIG. 4.

This way, a long-delay time may be achieved with a small capacitor 128and a very fast reset time is also available.

This fast reset time is due to the switching action of the transistor132 and the relatively low resistance value of the resistor 160. Thelong delay time to reach Darlington turn on voltage is due to the largevoltage swing which the capacitor must undergo before the Darlingtonturn on voltage is reached. This is because of a high-impedance pathdefined by of voltage also is due to the fact that the capacitor 128 isinitially charged, at the base of the Darlington amplifier 106, negativewith respect to ground.

The primary function of the unidirectional current diodes 124, 138 inthe circuit is to insure that only one component (either the solenoidvalve or the electric motor driven air pump) is turned on when theDarlington pair 106 is turned on.

When the switch 90 is closed by a large load increase on the vehicle aperiod of time elapses until the Darlington turn on voltage is reached.When this occurs the solenoid valve 74 opens and, as shown in FIG. 1,high-pressure fluid from within the tank 54 passes through the conduit44 into both of the auxiliary load supporting devices 12, 14 therebyproducing a resultant uplifting force on the chassis of the vehicle thatsupplements that of the primary coil spring to return the vehiclechassis to its desired level operating position.

When the vehicle is unloaded the motor control switch 88 is closed, andafter it remains closed for the same specified length of time, thecompressor motor 5 6 isenergized. However, the compressor motor currentdoes not pass through the Darlington amplifier 106. The amplifier doescarry current through the energization circuit for the relay coil whichcauses armature 158 of the relay 68 to be pulled in a direction to closethe relay contacts to complete the energization circuit for the motor56. This arrangement avoids the need for using a large solid-stateswitching device capable of carrying the energization current of thepump motor which is in the order of 28 amperes. V

In one working embodiment of the above-described circuit, the'electricaland mechanical components have the following ratings:

Item Ruling Resistor I16 200 kn Capacitor 128 S0 ml'd. Transistor I32GE-2N5l72 Resistor I44 l0 kl) Resistor 14B 2 kn Resistor 160 l H1 in theaforementioned circuit, the time delay function provided by the RCcircuit defined by resistor 126 and capacitor 128 is five seconds. I

Another feature of this arrangement is that the Darlington amplifier 106can be triggered in a range from 1 to 1.6 volts depending upon thetemperature condition of operation, 'even with the charging sourcevarying in the range from 10 to 15 volts.

Another advantage is that the ratio of the reset bias resistor 160 tothe timing circuit resistor 126 is l to 200 l/200) which allows thecapacitor to be recharged to an initial negative battery voltage at thebase of the Darlington amplifier 106 in much shorter period of time thanthe lO-second timing period that it takes to charge the Darlingtonamplifier l06.to a turn on voltage through the timing circuit defined byresistor 126, capacitor [28 and the transistor 132. [n this way a longtime delay can be achieved with a small low-cost capacitor and a fastreset time is available because of the switching action of the low costtransistor 132.

Because of this ratio the charging time to turn on the Darlingtonamplifier 106 is in the order of ten seconds and the reset time is inthe order of one-fourth second which in effect is instantaneous insofaras the operational characteristics of the mechanical leveling system isconcerned.

While the embodiments of the present invention, as herein disclosed,constitute a preferred form, it is to be understood that other formsmight be adopted.

What is claimed is:

l. A control circuit for selective energization of first and secondelectrical components comprising; first and second power input terminaladapted to be electrically connected to the first and second electricalcomponent respectively, a solidstate switching device adapted to beconnected to each of said electrical components for regulating currentflow therethrough from said first and second power terminals, means forcontrolling conductivity of said solid-state switching device includingtimer means, means including a first diode and a second diode forconnecting said first and second power terminals respectively to saidtimer means for initiating a predetermined time delay cycle when eitherone of said first and second power terminals is connected to a powersource, and said diodes preventing crosscurrent energization of one ofsaid electrical components form the power terminal of the other of saidelectrical components, said timer means being responsive to apredetermined signal from said power terminals to condition said solidstate switching device to produce delayed energization of one or theother of the electrical components when the power terminal thereto isconnected to a power source, and reset means for resetting said timermeans when the signal from one or the other of said power terminals isinterrupted whereby energization of one or the other of said electricalcomponents only follows a predetermined fixed time period followingconnection of one or the other of said power terminals is to a powersource, said reset means including a transistor element having itscollector connected to said timer means and having its base emitterjunction connected by said diodes to said power terminals.

2. An electrical circuit for controlling energization of first andsecond electrical components in a vehicle-leveling system comprising;first static switching means for controlling the energization of each ofcomponents, timer means for controlling conductivity of said switchingmeans following a predetermined delay period, power circuit means fordirecting a predetermined signal to said timer means reflecting an aboveheight position of the leveling system, said first power circuit meansand said static switching means together forming an energization circuitfor one of said components, second power circuit means for directing asecond signal to said timer means when the leveling system is belowlevel, said second power circuit means and said solid state switchingdevice defining a second energization circuit for said component, meansfor preventing cross current flow of the signal in either of said firstor second power supply circuits to the other of said components as oneor the other of said signals is directed to said timer means, secondstatic switching means controlling said timer means to initiate a timedelay cycle when a signal is imposed on either of said power circuitmeans, said timer means turning on said first static switching meansfollowing a predetermined time delay, said second static switching meansturning off immediately when a signal is no longer on said first orsecond power circuit means, and resistance means connected to a powersource to reset said timer means to maintain a constant time delay priorto energization of said com ponents.

3. Anelectronic control circuit for regulating energization of a motorcontrol relay and a solenoid operated valve comprising; a three terminalswitching device having the anode terminal'thereof adapted to beelectrically connected to electrically energizable components of saidmotor control relay and said solenoid operated valve, first and secondswitch means electrically connecting each of said energizable componentsto a power source, means including said first and second switch meansand said three-terminal switching device for selectively energizing saidcomponents, timer means for controlling conductivity of saidthree-terminal switching device including a resistance and capacitor anda second three-terminal switch device for controlling charging of saidcapacitor, means for maintaining said second three-terminal switchingdevice conductive to charge said capacitor when said first or secondswitch means electrically connects either of said electrical componentsto the power source, said capacitor having its cathode terminalconnected to the control terminal of said first three terminal switchingdevice and being charged through said conductive second switching devicefrom a negative voltage relative to the power source at the cathodeterminal of said capacitor to a predetermined positive voltage at thecathode terminal to produce an extended delay period followingconnection of said components to the power source before said componentsare energized, a pair of diodes connected between said timer means andeach of said electrically energizable components to insure that only onecomponent is energized when said first three-terminal switching deviceis turned on, and means for resetting said capacitor at a ratesubstantially greater than the charge rate to charge said capacitor fromnegative to positive, said reset means including said secondthree-terminal switching device and a low-impedance path from said powersource.

4. An electronic control circuit for regulating energization of anelectrically energizable component comprising; a threeterminal switchingdevice having the anode terminal thereof adapted to be electricallyconnected to the electrically energizable component, a power source,switch means for electrically connecting said energizable component tosaid power source, means including said switch means and saidthree-terminal switching device for selectively energizing saidcomponent, timer means for controlling conductivity of saidthreetenninal switching device including a resistance and capacitor anda second three-terminal switching device having its input tenninalconnected in series with the positive terminal of said capacitor and itsoutput terminal connected to ground for charging of said capacitor,means for maintaining said second three-terminal switching deviceconductive to charge said capacitor when said switching meanselectrically connects said component to the power source, said capacitorhaving its cathode terminal connected to the control terminal of saidfirst three-terminal switching device and being charged through saidconductive second switching device from a negative voltage relative tothe power source at the cathode terminal of said capacitor to apredetermined positive voltage at the cathode terminal to produce anextended delay period following connection of said component to thepower source before said component is energized, and reset meansincluding a bias resistor continuously connected between said powersource and the junction between the positive terminal of said capacitorand the input terminal of said second switching device for charging saidpositive tenninal of said capacitor to a negative voltage relative tosaid power source at a charge rate substantially greater than the chargerate to charge said capacitor from negative to positive, said resetmeans being operative when said second three-terminal switching deviceis nonconductive for maintaining a continuous current path from saidpower source to the positive terminal of said timer means capacitor,said reset bias resistor having a resistance value substantially lessthan that of said timer means resistance to cause the positive terminalof said capacitor to be quickly recharged to the voltage of said powersource to produce an initial negative voltage at the control terminal ofsaid first-mentioned three terminal switching device equal to thevoltage of said power source whereby a long-time delay control can beobtained with a smaller capacitor.

ggyggg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No.3 624, 4-56 Dated November 13 1971 Invenport'g) James O.

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

Column 1, line 13, delete "of";

line 71, "react" should be reset Column 2, line 69, "invention" shouldbe connected Column 3, line 11, "shown" should be showing Column 4, line1 "indicates" should be includes I line 75, "test" should be resetColumn 6, line 15, delete the hyphen between"long-delay"y Column 7, line3, insert a before "much" line 33, "form" should be from line 52, insertsaid before "components"; line 62, insert second before "component";Column 8, line 13, "switch" should be switching line 50, "switching"should be switch Signed and sealed this 22nd day of August 1972.

(SEAL) Attest:

EDWARD M.l+LL1:'I Ji iiR,JR. ROBERT GOTTSCHALK glttesti mg OfficerCommissioner of Patents

1. A control circuit for selective energization of first and secondelectrical components comprising; first and second power input terminaladapted to be electrically connected to the first and second electricalcomponent respectively, a solid-state switching device adapted to beconnected to each of said electrical components for regulating currentflow therethrough from said first and second power terminals, means forcontrolling conductivity of said solid-state switching device includingtimer means, means including a first diode and a second diode forconnecting said first and second power terminals respectively to saidtimer means for initiating a predetermined time deLay cycle when eitherone of said first and second power terminals is connected to a powersource, and said diodes preventing crosscurrent energization of one ofsaid electrical components form the power terminal of the other of saidelectrical components, said timer means being responsive to apredetermined signal from said power terminals to condition said solidstate switching device to produce delayed energization of one or theother of the electrical components when the power terminal thereto isconnected to a power source, and reset means for resetting said timermeans when the signal from one or the other of said power terminals isinterrupted whereby energization of one or the other of said electricalcomponents only follows a predetermined fixed time period followingconnection of one or the other of said power terminals is to a powersource, said reset means including a transistor element having itscollector connected to said timer means and having its base emitterjunction connected by said diodes to said power terminals.
 2. Anelectrical circuit for controlling energization of first and secondelectrical components in a vehicle-leveling system comprising; firststatic switching means for controlling the energization of each ofcomponents, timer means for controlling conductivity of said switchingmeans following a predetermined delay period, power circuit means fordirecting a predetermined signal to said timer means reflecting an aboveheight position of the leveling system, said first power circuit meansand said static switching means together forming an energization circuitfor one of said components, second power circuit means for directing asecond signal to said timer means when the leveling system is belowlevel, said second power circuit means and said solid state switchingdevice defining a second energization circuit for said component, meansfor preventing cross current flow of the signal in either of said firstor second power supply circuits to the other of said components as oneor the other of said signals is directed to said timer means, secondstatic switching means controlling said timer means to initiate a timedelay cycle when a signal is imposed on either of said power circuitmeans, said timer means turning on said first static switching meansfollowing a predetermined time delay, said second static switching meansturning off immediately when a signal is no longer on said first orsecond power circuit means, and resistance means connected to a powersource to reset said timer means to maintain a constant time delay priorto energization of said components.
 3. An electronic control circuit forregulating energization of a motor control relay and a solenoid operatedvalve comprising; a three terminal switching device having the anodeterminal thereof adapted to be electrically connected to electricallyenergizable components of said motor control relay and said solenoidoperated valve, first and second switch means electrically connectingeach of said energizable components to a power source, means includingsaid first and second switch means and said three-terminal switchingdevice for selectively energizing said components, timer means forcontrolling conductivity of said three-terminal switching deviceincluding a resistance and capacitor and a second three-terminal switchdevice for controlling charging of said capacitor, means for maintainingsaid second three-terminal switching device conductive to charge saidcapacitor when said first or second switch means electrically connectseither of said electrical components to the power source, said capacitorhaving its cathode terminal connected to the control terminal of saidfirst three-terminal switching device and being charged through saidconductive second switching device from a negative voltage relative tothe power source at the cathode terminal of said capacitor to apredetermined positive voltage at the cathode terminal to produce anextended delay period following connection of saId components to thepower source before said components are energized, a pair of diodesconnected between said timer means and each of said electricallyenergizable components to insure that only one component is energizedwhen said first three-terminal switching device is turned on, and meansfor resetting said capacitor at a rate substantially greater than thecharge rate to charge said capacitor from negative to positive, saidreset means including said second three-terminal switching device and alow-impedance path from said power source.
 4. An electronic controlcircuit for regulating energization of an electrically energizablecomponent comprising; a three-terminal switching device having the anodeterminal thereof adapted to be electrically connected to theelectrically energizable component, a power source, switch means forelectrically connecting said energizable component to said power source,means including said switch means and said three-terminal switchingdevice for selectively energizing said component, timer means forcontrolling conductivity of said three-terminal switching deviceincluding a resistance and capacitor and a second three-terminalswitching device having its input terminal connected in series with thepositive terminal of said capacitor and its output terminal connected toground for charging of said capacitor, means for maintaining said secondthree-terminal switching device conductive to charge said capacitor whensaid switching means electrically connects said component to the powersource, said capacitor having its cathode terminal connected to thecontrol terminal of said first three-terminal switching device and beingcharged through said conductive second switching device from a negativevoltage relative to the power source at the cathode terminal of saidcapacitor to a predetermined positive voltage at the cathode terminal toproduce an extended delay period following connection of said componentto the power source before said component is energized, and reset meansincluding a bias resistor continuously connected between said powersource and the junction between the positive terminal of said capacitorand the input terminal of said second switching device for charging saidpositive terminal of said capacitor to a negative voltage relative tosaid power source at a charge rate substantially greater than the chargerate to charge said capacitor from negative to positive, said resetmeans being operative when said second three-terminal switching deviceis nonconductive for maintaining a continuous current path from saidpower source to the positive terminal of said timer means capacitor,said reset bias resistor having a resistance value substantially lessthan that of said timer means resistance to cause the positive terminalof said capacitor to be quickly recharged to the voltage of said powersource to produce an initial negative voltage at the control terminal ofsaid first-mentioned three terminal switching device equal to thevoltage of said power source whereby a long-time delay control can beobtained with a smaller capacitor.